Valve stem seals are used in a variety of internal combustion engines, for example in automobiles, in trucks, or in motorcycles, and serve to keep oil, which lubricates the camshaft, etc., and is circulating within the space defined by the valve head and valve cover, away from the combustion chamber and the intake system, as well as to prevent exhaust gas or pressurized fuel mixture from leaking into the space within the valve cover.
Due to the increased use of turbo chargers and compressors in automobiles, the number of applications has also increased in which the gas pressure on the side of the valve or valve stem seal facing towards the cylinder is significantly greater than the ambient pressure normally prevailing within the valve cover. In such applications, there is increased risk of “blow-by,” i.e. gas that leaks around the valve stem guide into the space within the valve cover and thereby impairs the lubrication of the valve. Conventional valve stem seals usually have a single seal lip for sealing the valve seat or the intake or exhaust region relative to the oil chamber of the valve cover. Therefore, “blow-by” can be caused, for example, by the large pressure difference therebetween that lifts the seal lip away from the valve stem during operation.
Previous solutions for eliminating “blow-by” have increased the elastic or spring force that presses the seal lip for sealing the oil chamber against the valve stem, in order to better prevent the seal lips from lifting away from the valve stem during operation. However, these solutions are disadvantageous, because the increased pressing force also causes increased friction, thereby resulting in undesirable power losses and increased wear caused by the increased friction.
In addition, previous solutions for preventing blow-by have provided a second seal lip for sealing the valve stem relative to the gas-filled volume of the intake or exhaust system. In such solutions, the seal lip for sealing the gas chamber is supported on an inflexible support element, which, in order to withstand the gas pressure, concentrically surrounds the valve stem seal and connects the valve stem seal with the seal seat. However, this only allows the seal lip to compensate for a small radial play. Moreover, even if only a small radial play or misalignment between the valve stem and the valve stem guide exists, blow-by can still result.